JPS6213854B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an FM radio receiver equipped with a band muting circuit and a tuning point indicating circuit.

FM radio receivers not only receive FM signals, demodulate them, and output them, but they also have a tuning instruction device to make it easier for listeners to select a station, and they also have a tuning instruction device that allows listeners to tune in easily when there is no signal or when the received signal level is extremely low. Equipped with a level muting function that attenuates or cuts off the output when good reception characteristics cannot be obtained, or
It is equipped with a band muting function that attenuates or cuts off the output when a good demodulated output cannot be obtained because the received signal frequency is not accurately tuned. Additionally, some electronically tuned FM radio receivers have a function that automatically stops sweeping the receiving frequency and tunes to the broadcast station.

In order to realize the function of turning on a lamp near the tuning point or automatically stopping the sweep when there is a broadcast station, the level is high (or low) only in the vicinity of the tuning point, and low (low) at other received frequencies. It is necessary to create a signal (hereinafter referred to as SD signal) that will be at a high (or high) level in some way. Such conventional examples are shown in FIGS. 1 and 2.

In FIGS. 1 and 2, 1 is an antenna;
2 is the FM front end, 3 is the intermediate frequency stage, 14
is FM stereo demodulation circuit and low frequency amplification circuit,
15 and 15' indicate speakers. intermediate frequency stage 3
is a limiter amplifier 4, a signal level detection circuit 5,
It consists of an FM demodulation circuit 6, a window comparator 9, an OR circuit 10, and a muting circuit 13.

FIG. 1 shows an example of generating an SD signal 17 using a mutating circuit control signal (hereinafter referred to as a mutating signal) 11. Generally, the DC voltage 8 obtained by smoothing the FM demodulated output changes in proportion to the tuning frequency near the tuning point. This voltage 8 and
When comparing the reference voltage 7 of the FM demodulation circuit with the window comparator 9, the output of the window comparator 9 becomes low level only within a certain set voltage range, becomes high level when it deviates from that range, and becomes high level when it deviates further. When it goes out of band, it becomes low level again. On the other hand, although the output of the signal level detection circuit 5 is at a low level near the tuning point, it becomes a high level before the output of the window comparator 9 becomes a low level again. When the outputs of the level detection circuit 5 and the window comparator 9 are input to the OR circuit 10, the output 11 is as shown in Fig. 3-1.
As shown in , the signal becomes low level near the tuning point and becomes high level at other reception frequencies, and is used as a muting signal with a muting bandwidth W. This output 11 is an inverting amplifier circuit 16
Then, the level is inverted, and as shown in FIG. 3-2, an SD signal with an SD bandwidth WS is obtained which is high level near the tuning point and low level elsewhere.

This conventional example has the advantage that the mutating signal 11 and the SD signal 17 can be obtained relatively easily, but on the other hand, it is necessary to narrow the bandwidth WS of the SD signal 17, so the mutating bandwidth W must be narrowed. However, this also made tuning operations difficult, and when the depth of FM modulation became deep, the problem was that muting was common even though reception was good. On the other hand, when the muting bandwidth is widened, the tuning point indicator lamp lights up over a wide frequency range, making the tuning point unclear, and in the case of electronically tuned receivers, sweeping at frequencies other than the tuning point is possible. This caused the inconvenience of stopping.

A second conventional example devised to solve these inconveniences is shown in FIG. In this case, the output of the limiter amplifier 4 is amplified by a buffer amplifier 18, and is input to a bandpass filter 19 that passes only frequencies near the tuning range. When the output of the bandpass filter 19 is amplified by a buffer amplifier 20 and amplitude detected by an amplitude detector 21, an SD signal 17 as shown in FIG. 3-2 is obtained. In this case, the bandwidth of the mutating signal 11 and the bandwidth of the SD signal 17 can be set separately, and it is also applicable to a receiver that does not have a muting signal detection circuit including the level detector 5, window comparator 9, and OR circuit 10. However, the disadvantage is that the circuit becomes complicated and the cost increases. Furthermore, cases were likely to occur where the center frequency of the FM demodulation circuit 6 and the center frequency of the SD signal 17 did not match.

It is an object of the present invention to solve these drawbacks, to enable a simple circuit configuration, to set the muting bandwidth and the SD signal bandwidth separately, and to set the center frequency of these separately. The idea is to get an FM radio receiver that allows you to always be in tune.

According to the present invention, the reference voltage of the FM demodulation circuit and
A band detection circuit that detects the potential difference between the smoothed voltage of the FM demodulated output and obtains a voltage proportional to the absolute value of the difference between the optimum tuning frequency (tuning point) of the receiver and the tuning frequency, and a band detection circuit that has different set voltages. A muting circuit control signal is obtained by inputting the output of the band detection circuit to the first voltage comparison circuit, and the output of the band detection circuit is input to the second voltage comparison circuit. FM radio reception configured to output a tuning point instruction circuit control signal by inputting it to the circuit, allowing these bandwidths to be set independently and allowing these center frequencies to always match. Get a chance.

Next, the present invention will be explained in more detail with reference to the drawings.

Figure 4 shows one embodiment of the present invention.
8, 10, 12 to 15 are as explained in FIGS. 1 and 2.

Generally, the DC voltage 8 obtained by smoothing the output of the FM demodulation circuit 6 changes in proportion to the tuning frequency near the tuning point. Further, the value of the DC voltage 8 at the tuning point matches the reference voltage 7 of the FM demodulation circuit 6. The band detection circuit 22 is a circuit that uses these voltages 7 and 8 to generate a DC voltage proportional to the absolute value of the deviation from the tuning point, and a detailed example of the circuit is shown in FIG.

In Figure 5, 28 and 32 are electrolytic capacitors, 3
3, 36, 37, 42 are resistances, 29, 31, 3
9 and 40 are transistors, 35 and 38 are diodes, 41 and 43 are constant current circuits, 44 is a power supply terminal,
45 indicates the output of the band detection circuit 22.

The band detection circuit 22 has two input terminals, one of which receives the DC voltage 8 obtained by smoothing the output 34 of the FM demodulation circuit 6, and the other of which receives the DC voltage 8 obtained by smoothing the output 34 of the FM demodulation circuit 6.
A reference voltage 7 of the FM demodulation circuit 6 is input. A potential difference between these inputs occurs across resistor 30. At the tuning point, if there is no difference in potential between them, the emitter voltages of transistors 29 and 31 are equal, and the emitter voltages of transistors 39 and 40 are also equal. Therefore, the collector currents of the transistors 39 and 40 hardly flow, and the voltage 45 generated across the resistor 42 also becomes almost zero. Next, the tuning goes out and the DC voltage is 8
becomes higher than the reference voltage 7, the transistor 31
Since the emitter voltage of transistor 29 becomes higher than that of transistor 29, transistor 40 becomes
The transistor 39 becomes OFF, and the transistor 39 becomes operative. Therefore, a collector current proportional to the input voltage 8 flows through the transistor 39, and a voltage proportional to this is generated in the resistor 42. Further, when the tuning shifts in the opposite direction and the DC voltage 8 becomes lower than the reference voltage 7, the emitter voltage of the transistor 31 becomes lower than the emitter voltage of the transistor 29, so the transistor 39 is turned off and the transistor 40 is turned off. Becomes operational. Therefore, a collector current inversely proportional to the input voltage 8 flows through the transistor 40, and a voltage proportional to this flows across the resistor 42. In this way, whether the voltage at the input 8 of the band detection circuit 22 becomes higher or lower than the reference voltage 7, in other words, whether the tuning frequency becomes higher or lower than the tuning point, the band detection circuit The output 45 of 22 will be high and the ratio will be
increases in proportion to the absolute value of the potential difference.

When the synchronization goes further out of the band of the FM demodulation circuit 6, the output 45 of the band detection circuit 22 becomes low level again, but at that time the output of the level detection circuit 5 becomes high level, so the OR circuit 1
The output 23 of 0 becomes high level. This situation is shown in Figure 6-1.

The output 23 of the OR circuit 10 is set to a different comparison voltage 2
The voltage is input to two voltage comparison circuits 24 and 25 having voltages 6 and 27. Here, the comparison voltage 26 is changed to the comparison voltage 27
If this is set higher and added to the negative phase input of the voltage comparison circuit 24 and the OR circuit output 23 to the common mode input, near the tuning point, the output 2 of the OR circuit 10
3 is lower than the comparison voltage 26, the voltage comparison circuit 2
The output of No. 4 becomes low level. out of tune point
When the output 23 of the OR circuit 10 becomes higher than the comparison voltage 26, the output becomes high level. With such a configuration, a muting signal 11 with a wide bandwidth W can be generated as shown in FIG. 6-3. Furthermore, the comparison voltage 27 set low is connected to the common mode input terminal of the voltage comparison circuit 25, and the OR circuit 10
When the output 23 of is added to the negative phase input terminal, Figure 6-2
As shown in the figure, it is possible to create an SD signal with a narrow bandwidth WS.

In the present invention, the muting signal 11 and the SD signal 17 are output from the output 2 of the OR circuit 10 which is the same output.
3, the center frequencies of these signals always match.

[Brief explanation of the drawing]

FIGS. 1 and 2 are block diagrams showing examples of conventional circuits, and FIG. 3 is a diagram showing their characteristics. FIG. 4 is a block diagram showing the configuration of an embodiment of the present invention, and FIG. 5 is a circuit diagram of a band detection circuit.
FIG. 6 is a diagram showing the output characteristics of the present invention. 1...Antenna, 2...Front end, 3...
...Intermediate frequency stage, 4...Limiter amplifier, 5...Signal level detection circuit, 6...FM demodulation circuit, 7...
Reference voltage of the FM demodulation circuit, 8... Voltage obtained by smoothing the output of the FM demodulation circuit, 9... Window comparator, 10... OR circuit, 11... OR circuit output or muting signal, 12... Muting circuit input, 13 ...Muuting circuit, 14...
FM stereo demodulation, 15, 15'...speaker,
16... Inverting amplifier circuit, 17... Output or SD signal of the inverting amplifier circuit, 18, 20... Buffer amplifier, 19... Band pass filter, 21... Amplitude detection circuit, 22... Band detection circuit, 23... OR
Circuit output, 24, 25...Voltage comparison circuit, 26,
27... Setting voltage of the voltage comparison circuit, 28, 32...
...Electrolytic capacitor, 30, 33, 36, 37, 4
2... Resistor, 29, 31, 39, 40... Transistor, 35, 38... Diode, 41, 43
... Constant current circuit, 44 ... Power supply terminal, 45 ... Band detection circuit output, 34 ... FM demodulation circuit output.

Claims (1)

[Claims] 1 means for obtaining a voltage proportional to the difference between the optimum tuning frequency of the receiver and the currently received tuning frequency from the demodulation output of the demodulation circuit;
and means for comparing the proportional voltage with a second comparison voltage to obtain a tuning point indicating circuit control signal. .